1. Field of the Invention
The present invention relates generally to inter-cell handover techniques for time-division multiple access (TDMA) cellular mobile communication systems, and more specifically to a technique for synchronizing a mobile station to adjacent cell-site base stations during handover operation. The present invention is particularly useful for power-saving the battery consumption of TDMA mobile stations.
2. Description of the Related Art
Japanese Laid-Open Patent Specification Hei-4-371028 discloses a mobile station for a TDMA cellular communication system. During periodic idle slots, the mobile station receives a signal from a base station adjacent the current, communicating base station. From the received signal, the mobile station detects the identifier of the adjacent station and stores it in memory. At the same time, a frame number sent from this base station is also detected and stored in the memory. The stored frame number is then compared with a frame number received from the communicating base station and an inter-frame difference is detected between the two base stations. This process is repeated for all adjacent base stations. The detected inter-frame difference data are mapped in a table to individual base stations. When the mobile station receives a handover command signal from one of the base stations, it reads out corresponding frame difference data from the mapping table to adjust its timing.
Since the prior art requires the mobile station to constantly monitor the idle slots to collect timing data from surrounding base stations, it suffers considerable battery consumption. In addition, the prior art requires the mobile station to be equipped with sufficient hardware to process the received signals. Further, the prior art technique takes time to collect timing data since the mobile station hunts for a synchronization signal from a non-communicating base station at period idle slot intervals.